With the rapid development of aerospace industry, it is urgent to improve the efficiency of power system and reduce the energy consumption. A hollow thin-walled component with variable cross-sections, e.g., air inlet and spray tube, is a typical representive component widely used in aerospace vehicles, which is demanding and difficult to be manufactured. Ti2AlNb-based alloys have high room-temperature ductility and fracture toughness, excellent high temperature properties such as creep resistance, fatigue resistance and oxidation resistance, as well as the advantages such as low density, low coefficient of thermal expansion and non-magnetic properties. Therefore, it has become one of the most potential materials to replace the superalloy at the service temperature of 600-800° C., which is of great significance for further reducing the weight of aerospace vehicles and improving the payload and flight speed.
The key components (e.g., the air inlet and spray tube) in power system of air vehicles need to bear high speed and high pressure air scouring, and the service environment is very severe. The working temperature of the component body is up to 600-800° C. and the gas pressure endured by the component is usually several MPa (dozens of atmospheric pressure), with a maximum value of 20 MPa (two hundred atmospheres). Therefore, it is necessary for this kind of component to have excellent service performances at a high temperature, including high strength and certain fracture elongation. Meanwhile, in order to meet the requirement of aerodynamics, realize the control of inlet air flow field and avoid the risk of melt-through caused by the excessive aerodynamic heat at the stationary point, the requirement for the shape and dimension accuracies of components such as the air inlet and spray tube are very high, especially the requirement for the accuracy of the inner surface is harsh.
In the aspect of shape and dimension accuracy control, due to the combination manner in hybrid bonds of coexisted metal bond and covalent bond among Ti2AlNb-based alloy atoms, it has intrinsic brittleness and can only be formed at a high temperature. At the same time, since the hollow thin-walled components cannot be machined after forming, especially the inner surface of the components can hardly be machined, a high-temperature forming method with high accuracy is needed, which can directly meet the requirements of dimensional accuracy for surface during the forming process.
In terms of controlling the component's service performance, a Ti2AlNb-based alloy is composed of α2, B2 and O phases, wherein the intrinsic plasticity of the O phase is better than that of α2 phase. However, under the service condition, the internal crack of the component is easily formed at the equiaxed O/O phase grain boundaries, resulting in the intergranular fracture. Therefore, the content and morphology of the O phase have a significant effect on the high temperature service performance of Ti2AlNb-based alloy components. Accordingly, for achieving excellent usage performance, a heat treatment of Ti2AlNb-based alloy components is needed to be carried out after forming to optimize the microstructure (such as the content, morphology and size of O phase etc.).
However, the contradiction between the service performance control and the control to the accuracy of shape and dimension of Ti2AlNb-based alloy hollow thin-walled components is very prominent. It is found in the development process that, if the components are taken out of the die after hot forming and then heat treated, it will lead to serious shape distortion, the poor dimensional accuracy and the scrap product due to the evolution of the microstructure and the temperature variation during the heat treatment process. Therefore, it is urgent to develop a new technology for integrated forming and performance control of Ti2AlNb-based alloy hollow thin-walled components, so as to meet the impending needs of the aerospace aircraft development for Ti2AlNb-based alloy hollow thin-walled components with high performance and high accuracy.